Storage: configurable data dir for the external drive + daily DB prune

HOST_DATA_DIR in .env can now point /data at a host path (the 1TB
external drive) instead of the named volume, so odds history, caches
and snapshots stop eating the 128GB root disk. A daily prune drops
cache entries stale for over a week and ingest-log rows older than 14
days — faster polling no longer means unbounded DB growth.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/src/db/db.ts

@@ -135,6 +135,19 @@ export function cacheSet(key: string, value: string, ttl: number): void {
     .run(key, value, Date.now(), ttl);
 }
 
+/** Bound DB growth: drop cache entries stale for >7 days (the breaker only ever
+ *  serves recent staleness) and ingest-log rows older than 14 days. Returns the
+ *  number of rows removed. Runs daily from the scheduler. */
+export function prune(now = Date.now()): number {
+  const cache = db()
+    .prepare('DELETE FROM kv_cache WHERE ? - fetched_at > ttl + 7 * 86400000')
+    .run(now);
+  const log = db()
+    .prepare('DELETE FROM ingest_log WHERE at < ?')
+    .run(now - 14 * 86400000);
+  return Number(cache.changes) + Number(log.changes);
+}
+
 // ---- source health / circuit breaker ----
 export interface SourceHealthRow {
   source: string;